Systems for filtering fluid have been developed for use in a wide variety of commerical, industrial, and domestic applications. Some systems employ mechanical or physical barriers to block micropollutants, particulate, and other materials in the fluid. Other systems rely upon carbon to reduce materials in the fluid through adsorption or reduction-oxidation (redox) materials to induce electron transfers that reduce the content of a material in the fluid. Some systems even use a combination of the foregoing techniques to achieve the desired filtering, treatment, purification, or conditioning (collectively referred to herein as filtering) of the fluid.
As with the type of filtering process employed, the fluids to be filtered by different systems may vary widely. For example, the fluids may be gaseous or liquid, and may have relatively high or low viscosities. Further, the pressure of the fluid may vary greatly, above and below one atmosphere. As will be appreciated, each of these factors may influence the design and operation of a filter system.
One particular fluid of interest to be filtered is water. As will be appreciated, water has many industrial, commerical, and domestic uses in which some threshold level of purity is desirable. The most common example is the use of water in the home for drinking and cooking. The water available from many sources and distribution systems, however, is unsuitable for such uses because it includes contaminants such as particulates (e.g., scale, rust, soil, or sediment), micropollutants (e.g., giardia, salmonella, et cetera), bacteria, chemicals (e.g., chlorine, hydrogen sulfide, lead, trihalomethanes, and other inorganics). As a result, there has been a significant expansion in the world market for bottled water and water filter systems.
A conventional water filter system often includes a housing for receiving at least one filter element in a path of fluid flow defined by the housing. The filter element typically includes a shell or frame and a filter medium supported by the shell. Commonly used filter media include close-woven textiles, metal screens, string-wound fibers, papers, nonwoven fabrics, carbon granular beds, and various reduction-oxidation (redox) media.
Addressing the construction of several common filter elements in greater detail, one embodiment is cylindrical in shape and includes a paper filter medium or barrier, which may be rolled or folded around the perimeter of a porous cylindrical core. The core is seated against the housing at both ends and water flows radially through the assembly, while the paper filter blocks particulate.
Alternatively, the filter element or barrier may be formed by winding a suitable fiber or string about a perforate cylindrical core. Each end of the fiber wound about the core abuts a circular seal provided on the housing. Water flows radially between the wound fibers, which are spaced to block the desired contaminants.
In yet another embodiment, the filter element or cartridge is a cylindrical shell, filled with an adsorbent or electron transfer media. For example, the shell may contain a granulated activated carbon (GAC), such as charcoal. The shell is impermeable and coupled to the housing at both ends by seals, directing the flow of water axially through the GAC. The GAC, through adsorption, reduces or removes chlorine and its associated taste, as well as hydrogen sulfide and its associated odor from the water. The spacing between the granules, further, obstructs the flow of particulate in the water.
One of the most common problems with such conventional filter systems is their inability to remove small particulate at high filtration rates. Typically, a high filtration rate is achieved only by employing a number of independent filter elements in independent housings, significantly increasing system size and expense. Further, filter elements designed to remove small particulate will typically clog relatively quickly when exposed to larger particulate, requiring their frequent replacement.
Another problem with conventional systems of the type described above is that they are typically only suited for use in reducing or removing certain types of contaminants. More particularly, a given filter element may be suitable for use in filtering water including particulates but not chemicals, or may be suitable only for reducing certain types of chemicals. As a result, a filter system that works well in one part of the country may be completely inadequate in another geographic area.
In addition to having limited adaptability to various water conditions, many conventional filter systems are not readily placed in different physical environments. For example, when a filter system is to be used in the home, it may be desirable to locate the housing and filter element either above or below a kitchen or bathroom countertop. Conventional filter systems, however, are not readily adaptable for efficient use in these different locations.
In summary, it would be desirable to provide a low-cost system that is capable of filtering small particulate at a high volumetric rate, without frequent filter element replacement, and that is usable with a wide variety of fluid conditions and in a variety of environments.